Question

In: Chemistry

Physical Chemistry A)The electrolytic conductivity of 0.10 M solution of acetic acid is 5.3x 10-5 Scm-1....

Physical Chemistry

A)The electrolytic conductivity of 0.10 M solution of acetic acid
is 5.3x 10-5 Scm-1. The cell constant was 0.10 cm-1. Neglecting activity
coefficient, Calculate the acid dissociation constant (Ka).
(Λmo for acetic acid = 390. S cm2 mol-1)

B)The observed osmotic pressure of 0.1 M acetic acid solution is
2.45 atm at 25.0 oC. Calculate the Van’t Hoff factor (i) and the degree of
ionization (α). Compare your value with that obtained from problem 1.
Comment on your answer.

Solutions

Expert Solution

A). electrolytic conductivity, k = 5.3x 10-5 Scm-1

concentration, c = 0.10 M

cell constant = 0.10 cm-1

Λmo for acetic acid = 390. S cm2 mol-1

Λm = Λmo - k*

= 390 - 5.3 x 10-5 *

= 390 - 1.676 x 10-5

= 389.99

degree of dissociation, = Λm / Λmo

= 389.99 / 390

= 0.99

Acid dissociation constant, Ka = *c / (1 - )

= 0.992 * 0.10 / (1 - 0.99)

= 0.09801 / 0.01

= 9.801

Thus, acid dissociation constant, Ka = 9.801

B). Osmotic pressure, = 2.45 atm

concentration, c = 0.1 M

Temperature, T = 25 oC = 298 K

We know that -

= i *c*R*T

2.45 = i*0.1*0.0821*298

2.45 = i*2.446

i = 2.45 / 2.446

i = 1.0

Van't Hoff factor, i = 1.0

Acetic acid ionize as -

CH3COOH      CH3COO- + H+

Acetic acid ionize into 2 ions.

n = 2

1 = 1 + (2 - 1)

= 0

degree of ionization (α) = 0


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